Stacked integrated circuit leadframe package system

ABSTRACT

A stacked integrated circuit leadframe package system including forming a leadframe, packaging a top integrated circuit on a one side of the leadframe, packaging a bottom integrated circuit on an opposite side of the leadframe, and forming external electrical interconnects on the leadframe.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Divisional of co-pending U.S. application Ser. No.11/306,805 filed Jan. 11, 2006, which claims the benefit of U.S.Provisional Patent Application Ser. No. 60/652,346 filed Feb. 10, 2005,and the subject matter thereof is hereby incorporated herein byreference thereto.

TECHNICAL FIELD

The present invention relates generally to integrated circuit packagesystems, and more particularly to a system for a stacked integratedcircuit leadframe.

BACKGROUND ART

Integrated circuits are used in many portable electronic products, suchas cell phone, portable computers, voice recorders, etc. as well as inmany larger electronic systems, such as cars, planes, industrial controlsystems, etc. Across virtually all applications, there continues to bedemand for reducing the size and increasing performance of the devices.The intense demand is no more visible than in portable electronics thathave become so ubiquitous.

As electronic devices have become smaller and thinner, the packages forprotecting and interconnecting IC chips particularly power IC have thesame trend, too.

The goals in designing and manufacturing semiconductor devices have beento make the devices smaller, more complex, with higher densities, and toinclude additional features. One method that improves the features andthe densities of the semiconductor devices is to shrink the line sizesused in the lithographic process step in fabricating semiconductordevices. For example, each one-half reduction in line width of thecircuits of the semiconductor device corresponds to a four-fold increasein chip density for the same size device.

Unfortunately, increasing density simply through improved lithographictechniques is limited because of physical limits and the cost factor ofscaling down the dimensions of the semiconductor device. Accordingly,many attempts to increase semiconductor device density have beenpursued. One such alternative has been the stacking of multiplesemiconductor devices.

Thus a need still remains for an integrated circuit package system toprovide increasing density without sacrificing reliability, yield andhigh volume manufacturing processes. In view of the increasing demandfor density of integrated circuits and particularly portable electronicproducts, it is increasingly critical that answers be found to theseproblems.

Solutions to these problems have been long sought but prior developmentshave not taught or suggested any solutions and, thus, solutions to theseproblems have long eluded those skilled in the art.

DISCLOSURE OF THE INVENTION

The present invention provides a stacked integrated circuit leadframepackage system providing forming a leadframe, packaging a top integratedcircuit on a one side of the leadframe, packaging a bottom integratedcircuit on an opposite side of the leadframe, and forming externalelectrical interconnects on the leadframe.

Certain embodiments of the invention have other advantages in additionto or in place of those mentioned or obvious from the above. Theadvantages will become apparent to those skilled in the art from areading of the following detailed description when taken with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a stacked integrated circuitleadframe package system in an embodiment of the present invention;

FIG. 2A is a top plan view of a leadframe array prior to singulation;

FIG. 2B is a top plan view of the leadframe array prior to singulationin greater detail;

FIG. 3 is an isometric view of the stacked integrated circuit leadframepackage system of FIG. 1 without the electrical leads of FIG. 2A in adie attach phase;

FIG. 4 is a bottom plan view of the stacked integrated circuit leadframepackage system;

FIG. 5 is a top view the stacked integrated circuit leadframe packagesystem;

FIG. 6 is a cross-sectional view of a stacked integrated circuitleadframe package system 600 in an alternative embodiment of the presentinvention;

FIG. 7 is a cross-sectional view of a stacked integrated circuitleadframe package system in another alternative embodiment of thepresent invention;

FIG. 8 is a cross-sectional view of a stacked integrated circuitleadframe package system in yet another alternative embodiment of thepresent invention;

FIG. 9 is a cross-sectional view of a stacked integrated circuitleadframe package system in yet another alternative embodiment of thepresent invention;

FIG. 10 is a cross-sectional view of a stacked integrated circuitleadframe package system in yet another alternative embodiment of thepresent invention; and

FIG. 11 is a flow chart of a system of a system for a stacked integratedcircuit leadframe package in an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description, numerous specific details are given toprovide a thorough understanding of the invention. However, it will beapparent that the invention may be practiced without these specificdetails. In order to avoid obscuring the present invention, somewell-known circuits, and process steps are not disclosed in detail.

Likewise, the drawings showing embodiments of the system aresemi-diagrammatic and not to scale and, particularly, some of thedimensions are for the clarity of presentation and are shown greatlyexaggerated in the drawing FIGs. Similarly, although the sectional viewsin the drawings for ease of description show the invention with surfacesas oriented downward, this arrangement in the FIGs. is arbitrary and isnot intended to suggest that invention should necessarily be in adownward direction. Generally, the device can be operated in anyorientation. The same numbers are used in all the drawing FIGs. torelate to the same elements.

The term “horizontal” as used herein is defined as a plane parallel tothe conventional plane or surface of the invention, regardless of itsorientation. The term “vertical” refers to a direction perpendicular tothe horizontal as just defined. Terms, such as “on”, “above”, “below”,“bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”,“over”, and “under”, are defined with respect to the horizontal plane.

The term “processing” as used herein includes deposition of material orphotoresist, patterning, exposure, development, etching, cleaning,and/or removal of the material or photoresist as required in forming adescribed structure.

Referring now to FIG. 1, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 100 in an embodimentof the present invention. The stacked integrated circuit leadframepackage system 100 includes a leadframe 102 having a top surface 104 anda bottom surface 106. A top integrated circuit 108 is attached to thetop surface 104 of the leadframe 102 by a top adhesive 110. The topintegrated circuit 108 is electrically connected to the top surface 104by top bondwires 112. Similarly, a bottom integrated circuit 114 isattached to the bottom surface 106 of the leadframe 102 by a bottomadhesive 116. The bottom integrated circuit 114 is electricallyconnected to the bottom surface 106 by bottom bondwires 118.

An encapsulant 120 covers and protects the top integrated circuit 108,the bottom integrated circuit 114, the top bondwires 112, the bottombondwires 118 and the top surface 104. The encapsulant 120 partiallycovers and protects the bottom surface 106. Exposed regions of thebottom surface 106 may include a preparation, such as metal plating, forattaching electrical interconnects 122, such as solder balls.

Referring now to FIG. 2A, therein is shown a top plan view of aleadframe array 200 prior to singulation. The leadframe array 200includes electrical leads 202, a die pad 204, and a dam bar 206 for eachleadframe. The dam bar 206 provides location and spacing of theelectrical leads 202 of the leadframe 102 prior to encapsulation. Afterwire bonding and encapsulation, location and spacing of the electricalleads 202 are substantially fixed and the dam bar 206 is removed.Removing the dam bar 206 singulates the electrical leads 202 providingelectrical isolation of each of the electrical leads 202. Forillustrative purposes the leadframe array 200 is shown as a two by twoarray, although it is understood that the array may be of any quantityin either an x-dimension or a y-dimension.

Referring now to FIG. 2B, therein is shown a top plan view of theleadframe array 200 in greater detail. As in FIG. 2A, the leadframearray 200 includes the electrical leads 202, the die pad 204, and thedam bar 206. The leadframe array 200 further includes a first recess 208and a second recess 210, such as a dimple.

The first recess 208 and the second recess 210 may be formed subsequentto formation of the leadframe array 200, in a removal process, such as apartial chemical etch or a half etch. The first recess 208 and thesecond recess 210 provide regions for conformal encapsulation to holdthe electrical leads 202 and the die pad 204 in a substantially planarposition with respect to one another and the top integrated circuit 108as shown in FIG. 1 or the bottom integrated circuit 114 as shown inFIG. 1. Conformal encapsulation substantially prevents vertical movementin the electrical leads 202 and the die pad 204.

Referring now to FIG. 3, therein is shown an isometric view 300 of thestacked integrated circuit leadframe package system 100 of FIG. 1without the electrical leads 202 of FIG. 2A in a die attach phase. Thedie pad 204 of FIG. 2A includes a part of the top surface 104 of FIG. 1and a part of the bottom surface 106 of FIG. 1. The top surface 104 ofthe die pad 204 and the bottom surface 106 of the die pad 204 providemounting surfaces for the top integrated circuit 108 and the bottomintegrated circuit 114, respectively. The top adhesive 110 attaches thetop integrated circuit 108 to the top surface 104. In a similar manner,the bottom adhesive 116 attaches the bottom integrated circuit 114 tothe bottom surface 106.

Referring now to FIG. 4, therein is shown a bottom plan view 400 of thestacked integrated circuit leadframe package system 100. The stackedintegrated circuit leadframe package system 100 includes the electricalinterconnects 122 of FIG. 1 and the encapsulant 120 of FIG. 1 over thebottom integrated circuit 114 of FIG. 1 (not shown). The electricalinterconnect 122 are deposited on the bottom surface 106 of FIG. 1 ofthe leadframe 102 of FIG. 1, and adjacent to the encapsulant 120 overthe bottom integrated circuit 114. The electrical interconnects 122provide electrical connectivity to the next level in a system, such as aprinted circuit board, chip carrier or another integrated circuitpackage.

Referring now to FIG. 5, therein is shown a top view of the stackedintegrated circuit leadframe package system 100. The top of the stackedintegrated circuit leadframe package system 100 includes the encapsulant120 of FIG. 1 and an orientation mark 502. The encapsulant 120 coversthe top integrated circuit 108 (not shown), the top bondwires 112 (notshown) and the top surface 104 (not shown) of the leadframe 102 (notshown). The top integrated circuit 108, the top bondwires 112 and thetop surface 104 of the leadframe 102, are substantially enclosed by theencapsulant 120. The orientation mark is formed, such as by molding,applying an adhesive or etching, to provide a reference point withrespect to a horizontal or rotational position of the stacked integratedcircuit leadframe package system 100.

Referring now to FIG. 6, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 600 in analternative embodiment of the present invention. The stacked integratedcircuit leadframe package system 600 includes a leadframe 602 having atop surface 604 and a bottom surface 606. An adhesive layer (not shown),such as a coverlay tape, is attached to the bottom surface 606 of theleadframe 602 providing a planar surface across the leadframe 602. A topintegrated circuit 608 is attached to the adhesive layer in a plane ofthe bottom surface 606. The top integrated circuit 608 is electricallyconnected to the top surface 604 of the leadframe 602 by top bondwires610. A top encapsulant 612 covers and protects the leadframe 602, thetop integrated circuit 608 and the top bondwires 610.

After a curing process of the top encapsulant 612, the adhesive layer isremoved exposing the bottom surface 606 and the top integrated circuit608. A bottom integrated circuit 614 is attached to the top integratedcircuit 608 by an adhesive 616. The bottom integrated circuit 614 iselectrically connected to the bottom surface 606 by bottom bondwires618. A bottom encapsulant 620 covers and protects the bottom integratedcircuit 614 and the bottom bondwires 618. The bottom encapsulant 620partially covers and protects the bottom surface 606. Exposed regions ofthe bottom surface 606 may include a preparation, such as metal plating,for attaching electrical interconnects 622, such as solder balls. Theelectrical interconnects 622 are attached to the bottom surface 606 toprovide electrical connectivity to the next level in a system, such as aprinted circuit board, chip carrier or another integrated circuitpackage.

Referring now to FIG. 7, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 700 in anotheralternative embodiment of the present invention. The stacked integratedcircuit leadframe package system 700 includes a leadframe 702 having atop surface 704 and a bottom surface 706. An adhesive layer (not shown),such as a coverlay tape, is attached to the top surface 704 of theleadframe 702 providing a planar surface across the leadframe 702. Abottom integrated circuit 708 is attached to the adhesive layer in aplane of the top surface 704. The bottom integrated circuit 708 iselectrically connected to the bottom surface 706 of the leadframe 702 bybottom bondwires 710. A bottom encapsulant 712 covers and protects thebottom integrated circuit 708 and the bottom bondwires 710. The bottomencapsulant 712 partially covers and protects the bottom surface 706.

After a curing process of the bottom encapsulant 712, the adhesive layeris removed exposing the top surface 704 and the bottom integratedcircuit 708. A top integrated circuit 714 is attached to the bottomintegrated circuit 708 by an adhesive 716. The top integrated circuit714 is electrically connected to the top surface 704 by top bondwires718. A top encapsulant 720 covers and protects the leadframe 702, thetop integrated circuit 714 and the top bondwires 718. Exposed regions ofthe bottom surface 706 may include a preparation, such as metal plating,for attaching electrical interconnects 722, such as solder balls. Theelectrical interconnects 722 are attached to the bottom surface 706 toprovide electrical connectivity to the next level in a system, such as aprinted circuit board, chip carrier or another integrated circuitpackage.

Referring now to FIG. 8, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 800 in yet anotheralternative embodiment of the present invention. Similar to the stackedintegrated circuit leadframe package system 100 as shown in FIG. 1, thestacked integrated circuit leadframe package system 800 includes aleadframe 802 having a top surface 804 and a bottom surface 806. A topintegrated circuit 808 is attached to the top surface 804 of theleadframe 802 by a top adhesive 810. The top integrated circuit 808 iselectrically connected to the top surface 804 by top bondwires 812. Atop encapsulant 814 covers and protects the leadframe 802, the topintegrated circuit 808 and the top bondwires 812.

The stacked integrated circuit leadframe package system 800 alsoincludes a second leadframe 816 having a top surface 818 and a bottomsurface 820. A second integrated circuit 822 is attached to the topsurface 818 of the second leadframe 816 by a second adhesive 824. Thesecond integrated circuit 822 is electrically connected to the topsurface 818 by second bondwires 826. A second encapsulant 828 covers andprotects the second leadframe 816, the second integrated circuit 822 andthe second bondwires 826.

Planar dimensions of the second leadframe 816 are predetermined to besmaller than planar dimensions of the leadframe 802 less the planardimensions of electrical interconnects 832. Exposed regions of thebottom surface 806 of the leadframe 802 may include a preparation, suchas metal plating, for attaching the electrical interconnects 832, suchas solder balls. The electrical interconnects 832 are attached to thebottom surface 806 of the leadframe 802 to provide electricalconnectivity to the next level in a system, such as a printed circuitboard, chip carrier or another integrated circuit package.

An example of the above would be a combined large leadframe chip scalepackage (LFCSP) for the top and a small LFCSP for the bottom.

Referring now to FIG. 9, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 900 in yet anotheralternative embodiment of the present invention. Similar to the stackedintegrated circuit leadframe package system 100 as shown in FIG. 1, thestacked integrated circuit leadframe package system 900 includes aleadframe 902 having a top surface 904 and a bottom surface 906. A topintegrated circuit 908 is attached to the top surface 904 of theleadframe 902 by a top adhesive 910. The top integrated circuit 908 iselectrically connected to the top surface 904 by top bondwires 912. Atop encapsulant 914 covers and protects the leadframe 902, the topintegrated circuit 908 and the top bondwires 912.

A bump chip carrier (BCC) 916 having a second integrated circuit 918 isattached to the leadframe 902. Chip carrier bumps 920 and the leadframe902 are attached both mechanically and electrically with a bondingmaterial, such as plating metal. Planar dimensions of the bump chipcarrier 916 are predetermined to be smaller than planar dimensions ofthe leadframe 902 less the planar dimensions of electrical interconnects922. Exposed regions of the bottom surface 906 of the leadframe 902 mayinclude a preparation, such as metal plating, for attaching theelectrical interconnects 922, such as solder balls. The electricalinterconnects 922 are attached to the bottom surface 906 of theleadframe 902 to provide electrical connectivity to the next level in asystem, such as a printed circuit board, chip carrier or anotherintegrated circuit package.

An example of the above would be a large LFCSP for the top and a smallBCC for the bottom.

Referring now to FIG. 10, therein is shown a cross-sectional view of astacked integrated circuit leadframe package system 1000 in yet anotheralternative embodiment of the present invention. Similar to the stackedintegrated circuit leadframe package system 100 as shown in FIG. 1, thestacked integrated circuit leadframe package system 1000 includes aleadframe 1002 having a top surface 1004 and a bottom surface 1006. Atop integrated circuit 1008 is attached to the top surface 904 of theleadframe 902 by a top adhesive 1010.

In contrast to the stacked integrated circuit leadframe package system100 as shown in FIG. 1, a stacked-die integrated circuit 1012 isattached to the top integrated circuit 1008 by a second top adhesive1014. The top integrated circuit 1008 and the stacked-die integratedcircuit 1012 are electrically connected to the top surface 1004 by topbondwires 1016. Planar dimensions of the stacked-die integrated circuit1012 are predetermined to be smaller than planar dimensions of the topintegrated circuit 1008 less the planar dimensions of connectionregions, such as bond pads, for the top bondwires 1016.

Also similar to the stacked integrated circuit leadframe package system100 as shown in FIG. 1, a bottom integrated circuit 1018 is attached tothe bottom surface 1006 of the leadframe 1002 by a bottom adhesive 1020.The bottom integrated circuit 1018 is electrically connected to thebottom surface 1006 by bottom bondwires 1022. An encapsulant 1024 coversand protects the top integrated circuit 1008, the stacked-die integratedcircuit 1012, the bottom integrated circuit 1018, the top bondwires1016, the bottom bondwires 1022 and the top surface 1004.

Alternatively, an integrated circuit in a land grid array (not shown)may be used in place of the bottom integrated circuit 1018. Theintegrated circuit in a land grid array may be connected to the bottomsurface 1006 by bottom bondwires 1022, as well. The encapsulant 1024would be applied as above to cover and protect the integrated circuit ina land grid array.

Again similar to the stacked integrated circuit leadframe package system100 as shown in FIG. 1, the encapsulant 1024 partially covers andprotects the bottom surface 1006. Exposed regions of the bottom surface1006 may include a preparation, such as metal plating, for attachingelectrical interconnects 1026, such as solder balls. The electricalinterconnects 1026 are attached to the bottom surface 1006 to provideelectrical connectivity to the next level in a system, such as a printedcircuit board, chip carrier or another integrated circuit package.

An example of the above would be a LFCSP for the top and a small LFCSPor land grid array (LGA) package for the bottom.

Referring now to FIG. 11, therein is shown a flow chart of a system 1100for a stacked integrated circuit leadframe package in an embodiment ofthe present invention. The system 1100 includes forming a leadframe in ablock 1102; packaging a top integrated circuit on a one side of theleadframe in a block 1104; packaging a bottom integrated circuit on anopposite side of the leadframe in a block 1106; and forming an externalelectrical interconnects on the leadframe in a block 1108.

In greater detail, a method to fabricate the stacked integrated circuitleadframe package system 100, in an embodiment of the present invention,is performed as follows:

-   -   1. Forming a leadframe. (FIG. 1)    -   2. Mounting a top integrated circuit on a one side of the        leadframe. (FIG. 1)    -   3. Connecting the top integrated circuit to the one side of the        leadframe. (FIG. 1)    -   4. Encapsulating the top integrated circuit with the one side of        the leadframe. (FIG. 1)    -   5. Mounting a bottom integrated circuit on an opposite side of        the leadframe. (FIG. 1)    -   6. Connecting the bottom integrated circuit to the opposite side        of the leadframe. (FIG. 1)    -   7. Encapsulating the bottom integrated circuit with the opposite        side of the leadframe. (FIG. 1)    -   8. Depositing external electrical interconnects on the        leadframe. (FIG. 1)

It has been discovered that the present invention thus has numerousadvantages.

An advantage is that the present invention reduces the size of multipleintegrated circuit packages. The stacking of integrated circuits is morecompact and space efficient, particularly with respect to the footprintor planar dimension. The elimination of additional packages, evenchip-scale, provides significant size reductions.

It has been discovered that the disclosed structure provides higheroperating speeds. The size reduction also provides shorterinterconnections between integrated circuits and the next level systemor product, such as a printed circuit board, chip carrier or anotherintegrated circuit package. The shorter interconnections reduceparasitics and improve speed.

It has also been discovered that the disclosed structure providesimproved electrical performance between the integrated circuits.Minimizing the distance between multiple integrated circuits providessignificant improvements in electrical signals between the integratedcircuits.

Yet another discovery of the disclosed structure is improvements in thesystem or product. The compactness and space efficiency contribute toarea and volume improvements, and improved operating speeds andelectrical performance contribute to power and heat savings of theproduct.

Yet another discovery of the disclosed structure is compatibility tointegrated circuit die with both center pads and peripheral pads.Integrated circuits stacked on multiple surfaces and with multipleorientations, provide flexibility to accommodate multiple integratedcircuit input/output pad locations.

Yet another discovery of the disclosed structure is compatibility withseveral package types, such as leadframe, bump chip carrier and landgrid array. The stacking on multiple surfaces and multiple orientationsof active and non-active surfaces accommodates a variety of packagetypes.

Yet another discovery of the disclosed structure is improvedconnectivity between the protruding solder ball and the printed circuitboard. The solder interconnect provides improved manufacturing, such ascost, complexity, volume, yield and compatibility, over otherinterconnect technologies, such as land grid arrays.

Yet another discovery of the disclosed structure is improvements inmanufacturing yields and processes. The multiple integrated circuits maybe tested individually during intermediate phases of the processing.This prevents costly scrap of good integrated circuits after combiningfailed integrated circuits.

These and other valuable aspects of the present invention consequentlyfurther the state of the technology to at least the next level.

Thus, it has been discovered that the stacked integrated circuitleadframe system method and apparatus of the present invention furnishimportant and heretofore unknown and unavailable solutions,capabilities, and functional advantages. The resulting processes andconfigurations are straightforward, cost-effective, uncomplicated,highly versatile and effective, can be implemented by adapting knowntechnologies, and are thus readily suited for efficient and economicalmanufacturing.

While the invention has been described in conjunction with a specificbest mode, it is to be understood that many alternatives, modifications,and variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, it is intended to embrace allsuch alternatives, modifications, and variations, which fall within thescope of the included claims. All matters hithertofore set forth hereinor shown in the accompanying drawings are to be interpreted in anillustrative and non-limiting sense.

1. A stacked integrated circuit leadframe package system comprising: aleadframe; a top integrated circuit packaged on a one side of theleadframe; a bottom integrated circuit packaged on an opposite side ofthe leadframe; and external electrical interconnects on the leadframe.2. The system as claimed in claim 1 wherein the leadframe furthercomprises a leadframe array having multiple leadframes.
 3. The system asclaimed in claim 1 wherein the top integrated circuit packaged on theone side of the leadframe further comprises a further integrated circuitmounted on the top integrated circuit.
 4. The system as claimed in claim1 wherein: the top integrated circuit or the bottom integrated circuithas a surface substantially coplanar with a surface of the leadframe;and the top integrated circuit and the bottom integrated circuit arebonded together.
 5. The system as claimed in claim 1 wherein the bottomintegrated circuit further comprises a chip scale package attached tothe leadframe.
 6. An integrated circuit leadframe package systemcomprising: a leadframe; a top integrated circuit on a one side of theleadframe, the top integrated circuit electrically connected to the oneside of the leadframe and the top integrated circuit encapsulated withthe one side of the leadframe; a bottom integrated circuit on anopposite side of the leadframe, the bottom integrated circuit connectedto the opposite side of the leadframe and the bottom integrated circuitencapsulated with the opposite side of the leadframe; and externalelectrical interconnects on the leadframe.
 7. The system as claimed inclaim 6 further comprising a further leadframe attached to the oppositeside of the leadframe with the bottom integrated circuit attachedthereto.
 8. The system as claimed in claim 6 further comprising: afurther integrated circuit on the top integrated circuit; and anelectrical connection electrically connecting the further integratedcircuit to the one side of the leadframe.
 9. The system as claimed inclaim 6 wherein: the top integrated circuit or the bottom integratedcircuit has a surface substantially coplanar with a surface of theleadframe; and the top integrated circuit and the bottom integratedcircuit are bonded together.
 10. The system as claimed in claim 6wherein the bottom integrated circuit mounted on the opposite side ofthe leadframe further comprises the bottom integrated circuit in a bumpchip carrier or a land grid array package mounted on the opposite sideof the leadframe.